1. Field of the Invention
The present invention relates in general to a cell for use in a solid polymer electrolyte fuel cell that employs a solid polymer electrolyte membrane, and more particular to a cell for a solid polymer electrolyte fuel cell of novel construction that affords a high level of gas flow path sealing functionality within the cell by means of a simple construction.
2. Description of the Related Art
As is well known, solid polymer electrolyte fuel cells are able to produce electrical power by means of an electrochemical reaction when supplied with oxygen (air) as an oxidant and hydrogen as a fuel, these being supplied onto the surfaces of a pair of catalyst electrodes superposed against either face of an electrolyte which is a solid polymer electrolyte membrane, such as a solid ion exchange membrane or the like.
In solid polymer electrolyte fuel batteries, it is important that there be consistent supply of oxygen and hydrogen onto the surfaces of the catalyst electrodes in order to consistently and efficient produce the intended voltage. It is also important for the appropriate temperature to be maintained.
Accordingly, there is typically employed a cell of a structure wherein a membrane/electrode assembly (MEA) composed of a breathable porous membrane oxidant electrode and a fuel electrode disposed on either side of the solid polymer electrolyte membrane is assembled with a first separator superposed against the oxidant electrode face thereof and a second separator superposed against the fuel electrode face thereof. A plurality of such unit cells are stacked and electrically connected directly to produce the desired voltage.
An oxidant gas flow passage is formed by means of covering with the oxidant electrode a recess disposed on the first separator, and fuel gas flow passage is formed by means of covering with the fuel electrode a recess disposed on the second separator. A coolant flow passage is formed by a recess disposed in a secondary face of the first separator or second separator on the back side from a primary face which is superposed against the electrode, by covering the recess with the secondary face of another adjacent cell.
At respective peripheral edges of stacked unit cells, there are formed perforating therethrough in the stacking direction an oxidant gas inlet and an oxidant gas outlet, a fuel gas inlet and a fuel gas outlet, and a coolant inlet and a coolant outlet. Oxidant gas, fuel gas, and coolant supplied through these inlets and outlets are circulated the aforementioned oxidant gas flow passages, fuel gas flow passages, and coolant flow passages of the unit cells, and are discharged from the outlets (see JP-A-2002-83610, for example).
Here, the form of the oxidant gas flow passages and fuel gas flow passages has an important effect on efficiency and stability of power generation. Particularly in recent years, with the object of rapidly discharging the water which forms so as to prevent it from collecting, as well as to improve the efficiency of the electrochemical reaction, the pressure of the gases in the flow channels are sometimes set to high levels.
In solid polymer electrolyte fuel cells of conventional construction, it was difficult to ensure consistent sealing of the oxidant gas flow passage and the fuel gas flow passage that are formed on the superposed faces of the first separator and the second separator on either side of the membrane/electrode assembly. Thus, there was a risk that, for example, oxidant gas flowing to one side of the membrane/electrode assembly and fuel gas flowing to the other side could leak around the peripheral edge of the membrane/electrode assembly, resulting in problems such as power generation failure or abnormal generation of heat.
In view of such problems, unit cells of conventional design involve a separate seal rubber disposed between stacked elements (i.e. between the opposed faces of the first separator and the second separator against the membrane/electrode assembly). However, not only did including separate seal rubber components increase the number of parts and the number of assembly steps, but it was also difficult to position the seal rubber with accuracy.
When manufacturing cells for a solid polymer electrolyte fuel cell, it is necessary to superpose the first separator and the second separator against either face of the membrane/electrode assembly, but since the membrane/electrode assembly is difficult to handle due to its extreme thinness and low strength, there was also the problem of difficultly in correctly aligning the membrane/electrode assembly within the opposed faces of the first separator and the second separator.
In particular, the primary faces of the first and second separators have gas flow passages formed thereon, and at least one of the secondary faces has a coolant recess formed thereon. Therefore, if placement of the first and second separators should be misaligned with respect to the membrane/electrode assembly, for structural reasons, the intended gas flow passages or coolant flow passage will not be formed correctly, and in some instances may result in a drop in power generating ability or in gas leakage.